The present invention relates to a method for reducing electrostatic charging on the surface of shaped articles made of polyvinyl chloride resins and, in particular, to a new and useful method by which a very durable effect is obtained in reducing electrostatic charging on the surface of shaped articles made of polyvinyl chloride resins.
As is well known, polyvinyl chloride resins belong to one of the most important classes of thermoplastic synthetic resins, and shaped articles of the resin are widely employed in various applications.
One of the difficulties encountered in the use of shaped articles made of polyvinyl chloride based synthetic resins, is the outstanding tendency of these articles to be charged with static electricity which, in turn, results in a rapid loss of beauty in the appearance of the articles due to the adhesion or attraction of dust as well as in an unpleasant or sometimes dangerous effect to the human body, such as an electric shock by the electrostatic charges accumulated on the surface of the articles.
Various attempts have hitherto been made to reduce the accumulation of static electricity on the surfaces of shaped articles of polyvinyl chloride resins, including the application of an antistatic agent on to the surfaces and incorporation of an antistatic agent into the resin composition prior to fabrication of the resin composition, into the shaped articles. The surface application method of coating can give an instantaneous effect but is disadvantageous in the poor durability of its effectiveness as well as in the sticky touch of the surfaces which eventually leads to blocking of the shaped articles. The incorporation method is, on the other hand, better than the surface application method, in the durability of its antistatic effect, but the effectiveness is usually insufficient due to the limited amount of the antistatic agent incorporated in the shaped articles. When the amount of the antistatic agent incorporated is increased, a view toward obtaining a sufficient antistatic effect, the surfaces of these shaped articles also become sticky due to the bleeding of the antistatic agent leading to blocking of the shaped articles in addition to the problems of decreased heat resistance, poor workability and coloring and accelerated staining of the surfaces.
On the other hand, an attempt has been made to reduce the static electricity on the surfaces of shaped articles of polyvinyl chloride resins, by the treatment of the surface with low temperature plasma of a gas whereby the affinity of the surface with water can be enhanced. The antistatic effect obtained by this method is, however, not always satisfactory, especially, in its durability.